Suggest either adding an explanation what "if it is safe to do so" means, or refer to an explanation in the safe_to_use_settings_value?.

<pre>
# A "service" user or group that picks up values from settings when it is safe to do so (see {#safe_to_use_settings_value?}), and uses
# the given fallback value when not safe.
# @api private
#
</pre>